Ignition Coil for an Internal Combustion Engine

ABSTRACT

The invention relates to an ignition coil for an internal combustion engine. Said ignition coil comprises a primary coil base ( 2 ) carrying a primary winding ( 1 ) and having an especially cylindrical shape, a low voltage connection area ( 10 ) for connecting the primary winding ( 1 ) to a low voltage, a secondary winding ( 3 ) inductively coupled to the primary winding ( 1 ) and disposed on an especially cylindrical secondary coil base ( 4 ), for providing a high voltage for the spark plug of the internal combustion engine. The primary coil base ( 2 ) and the secondary coil base ( 4 ) are mounted concentric to one another. The ignition coil also comprises a high-voltage connection area ( 5 ) in which the secondary winding ( 3 ) contacts the spark plug. The aim of the invention is to improve the ignition coil of the aforementioned type with respect to its electromagnetic compatibility. For this purpose, an electrically conducting layer ( 16 ) which has a substantially cylindrical shape and mechanical damping properties is provided inside an annular space defined by the outer winding of the two windings ( 1, 3 ). Said layer is configured as a sandwich structure and consists of at least two partial layers ( 16   a,    16   b ) with an interposed intermediate layer ( 17 ).

The invention is directed to an ignition coil for an internal combustionengine with a substantially cylindrical primary coil base carrying aprimary winding, a low voltage connection area for the connection of theprimary winding to a low voltage, a secondary winding inductivelycoupled with the primary winding inductively and disposed on asubstantially cylindrical secondary coil base for providing a highvoltage for a spark plug of the internal combustion engine, wherein theprimary coil base and secondary coil base are positioned concentric toone another, and a high voltage connection area, in which the secondarywinding contacts the spark plug.

An ignition coil of this kind is known from DE 100 57 567.

With generic ignition coils, it concerns a so-called “rod coil forignition equipment of an internal combustion engine”, which includes along configuration, so that it can be positioned in the narrow, limitedspace available in the engine block of the internal combustion engine. Aprimary voltage is applied to the primary winding over the low voltagearea, which, as a result of the inductive coupling between the primaryand secondary winding, is available as a high transformed voltage to thehigh voltage connection area of the secondary winding and charges theignition coil there. With known ignition coils, a magnetic circuit isformed through the primary and secondary coil as well as the cylindricalmagnetic coil and the magnetically conductive shell. For the avoidanceof eddy current losses in the also metallic, conductive shell, the shellincludes a continuous lengthwise slit so that induced electrical eddycurrents are minimized.

An important functional feature of such an ignition coil is theso-called “electromagnetic compatibility” (EMC). In this connection, itis a matter of the opposing electromagnetic influence of transmittingand receiving devices. In conjunction with ignition coils, therequirements in relation to the EMC are particularly critical, forexample, it must be ensured that the emitted electromagneticinterference of the ignition coil may only indirectly or directly haveno or an acceptably low impact on the radio reception in the vehicle. Asa result of the arrangement of the normally open magnetic circuitsformed by the ignition coil and the used alternating current frequency,an adequate dampening of electromagnetic interference is not usuallyprovided with traditional ignition coils.

An ignition coil in accordance with the preamble of claim 1 is knownfrom DE 199 27 820 C1. Reference is further made to DE 199 09 211 A1 asprior art.

It is the object of the invention to improve an ignition coil of theabove-described kind with respect to its electromagnetic compatibility(EMC) and at the same time with respect to its mechanical stability.

This object is achieved in accordance with the invention in that anelectrically conductive, substantially cylindrical formed layer withmechanical dampening characteristics is located within an annular spacethat is defined by the outermost winding of the two windings. Theinvention is characterized in that a clear reduction of theelectromagnetic emitted interference can be achieved through theconductive layer, which is located between the primary and secondarycoils, without depleting the magnetic characteristics of the coil assuch. Thereby, the conductive layer located between the primary andsecondary coil has surprisingly no influence on the magneticcharacteristics of the ignition coil, but instead helps the ignitioncoil to a substantially improved shielding effectiveness.

It is further provided that the layer is formed as a sandwich structurecomprising at least two partial layers with a therebetween lyingintermediate layer with mechanical dampening characteristics.

Through the arrangement as a sandwich structure is not only theelectromagnetic compatibility (EMC) improved, but particularly also thestability of the ignition coil. The primary and secondary coils arecoupled relative to one another, namely in an advantageous manner,through the mechanical cushioning.

Further preferred embodiments are provided from the dependent claims.

The invention will be more specifically described in the following bymeans of an exemplary embodiment. Thereby illustrates:

FIG. 1 a longitudinal section through an ignition coil in accordancewith the exemplary embodiment of the invention;

FIG. 2 a a section along the line II-II in FIG. 1;

FIG. 2 b a section along the line IIb-IIb in FIG. 2 a;

FIG. 3 an enlarged view along the line III in FIG. 2 a.

FIG. 1 illustrates a longitudinal section through an exemplaryembodiment of an ignition coil in accordance with the present invention,which includes a low voltage connection 10 in its upper area, at whichthe ignition coil is charged with the required low voltage. In its lowerarea, the ignition coil includes a high voltage connection area 5, inwhich a connection segment meets a spark plug (not shown).

The ignition coil includes a cylindrical configuration. A cylindricalmagnetic core 6 is formed in the interior of the ignition coil andcomprises layered magnetic sheets, in particular silicon iron sheets.Several magnetic sheets of different widths are so stacked and connectedunder insulation of the individual sheets relative to one another toform the core 6 with an approximately circular contour. The core 6 issurrounded by a secondary coil base 4, which supports a secondarywinding 3 that is electrically connected with the high voltageconnection area 5. The connection of the secondary winding 3 with thehigh voltage connection area 5 is achieved through a substantiallyanti-interference serving resistor 11 and a rectifying diode 12, whichis housed in a housing 13.

The secondary coil base 4 is concentrically surrounded by a primary coilbase 2, which supports a primary winding 1. The primary winding 1 is athree-layered winding in the illustrated exemplary embodiment. The coilunit is surrounded by a sleeve 7, which comprises an electricallyconductive and at the same time magnetically conductive material, inparticular a silicon iron sheet.

In the illustrated embodiment, the sleeve 7 is formed by two roll-formedmagnetic sheets that are insulated from one another. The outercircumference of the sleeve 7 simultaneously forms the outer peripheryof the described ignition coil. The sleeve 7, the primary winding 1, thesecondary winding 3 and the core 6 form a magnetic circuit forgenerating the required ignition energy, with which the spark plug ischarged. The sleeve 7 is provided with a continuous, lengthwise slit forthe purpose of degrading eddy currents in the area of the magneticallyconductive sleeve 7. One of the supply leads of the primary winding 1extends along the lengthwise slit, namely that it is led out of theprimary coil base 2 in the lower area of the primary winding 1 and mustbe coupled with the low voltage connection 10, similar to the supplylead that is led from the upper side of the primary coil base 2. Thewinding lead running along the lengthwise slit 8 is at the same timefixed within a slit area through an insulation layer, in which thewinding lead is fixed in an appropriate embedding material. Theembedding is preferably achieved by means of epoxy resin.

The cylindrical formed area between the output of the ends of thesecondary winding 3 and the high voltage connection 5 serves on the onehand for the accommodation of the anti-interference serving resistor 11and on the other hand for the accommodation of the diode 12, throughwhich the rectification of the current flowing in the ignition coil isachieved, such that the negative impulse used for the ignition isallowed to pass, and the positive interfering impulse is, however,suppressed.

FIG. 2 a, b illustrate the layer 16 located between the two windings 1,3, which includes a lengthwise slit 18 for the abatement of eddycurrents.

FIG. 3 illustrates the construction of the layer 16 provided in theannular space between the primary and secondary coils in the form of asandwich structure. An intermediate layer 17 with absorptioncharacteristics is formed between two conductive layers 16a, 16b,wherein the intermediate layer 17 itself also contains conductiveparticles, which likewise impart conductive characteristics to theintermediate layer 17.

Through the layer 16, the ignition coil on the one hand achieves animproved EMC—compatibility as a result of the improved shieldingeffectiveness, and the primary and secondary coil bodies are, on theother hand, substantially better cushioned relative to one another. Thelayer 16 is therewith coupled with ground. Thus, interference voltages,which could capacitively overcouple from the secondary winding to theprimary winding, are electrically shorted. The connection of the layer16 with ground is achieved, such that one of the two sub-layers 16 a, 16b is electrically connected with the winding area of the primary winding1 lying on ground. For this, the primary winding 1 is not insulated atthe corresponding winding portion and through soldering or similarconnection techniques contacts the corresponding partial layer.Alternative thereto, a connection technique is also possible, by whichan additional conductor is provided, which couples the correspondingpartial layer 16 a, 16 b with the winding end of the primary coil 1.

1. An ignition coil for an internal combustion engine comprising: aprimary winding supporting substantially cylindrical primary coil base,a low voltage connection area for the connection of the primary windingto a low voltage, a secondary winding that is inductively coupled withthe primary winding and that is positioned on a substantiallycylindrical secondary coil base to provide a high voltage for a sparkplug of the internal combustion engine, wherein primary coil base andsecondary coil base are concentrically positioned relative to oneanother, and a high voltage connection area, in which the secondarywinding contacts the spark plug, wherein an electrically conductive,substantially cylinder formed layer with mechanical dampening propertiesis located within an annular space defined by the outermost winding ofthe two windings, and wherein the electrically conductive layer isformed as a sandwich structure comprising at least two partial layerswith a intermediate layer with mechanical dampening characteristicslying therebetween.
 2. An ignition coil for an internal combustionengine in accordance with claim 1, wherein the electrically conductivelayer is located in an annular space located between the primary windingand the secondary winding, which surrounds the innermost winding of thetwo windings.
 3. An ignition coil for an internal combustion engine inaccordance with claim 1, wherein the electrically conductive layersurrounds a magnetic core disposed within the innermost winding of thetwo windings.
 4. An ignition coil for an internal combustion engine inaccordance with claim 1, wherein at least one of the partial layers isformed as a foil.
 5. An ignition coil for an internal combustion enginein accordance with claim 1, wherein the intermediate layer iselectrically conductive.
 6. An ignition coil for an internal combustionengine in accordance with claim 5, wherein the electrically conductiveintermediate layer is electrically coupled with the ground of theignition coil.
 7. An ignition coil for an internal combustion engine inaccordance with claim 1, wherein the electrically conductive layerincludes a slot running in the lengthwise direction of the ignitioncoil.
 8. An ignition coil for an internal combustion engine inaccordance with claim 4, wherein the foil includes an arrangement ofopenings at regular intervals, in particular in the form of a latticenet.
 9. An ignition coil for an internal combustion engine in accordancewith claim 1, wherein the electrically conductive layer is roll formedfrom a flat material, such that an overlapping of the material occurs atthe adjoinment area.
 10. An ignition coil for an internal combustionengine in accordance with claim 1, wherein the contact of theelectrically conductive layer with one of the two windings is achievedthrough a separate contact means, in particular a supply lead, which thelayer (and the corresponding winding enclose.
 11. An ignition coil foran internal combustion engine in accordance with claim 1, wherein thecontact of the electrically conductive layer with one of the twowindings is achieved through direct contact of a conductive portion ofthe layer with an un-insulated portion of the corresponding winding.